Polymers of ethylene and propylene constitute important articles of commerce for numerous applications such as hose, belts, coated fabrics, wire insulation and jacketing, soles and heels, sponges, and passenger tires. These polymers, which display outstanding processing characteristics, have Mooney viscosities (ML-4/212.degree. F.) in the range of about 10 to 100. Unfortunately, in their uncured state, these polymers tend to flow in storage. The problem of cold-flow has been most acute with the lowest viscosity grades of such polymers although even the higher viscosity grades tend to exhibit this behavior during the warmer months of the year.
The problem of cold-flow is encountered in the storage of raw and uncured polymers which are generally stored in bags prior to use. During storage and transportation, the bags of raw polymers are stacked on top of each other in a cardboard carton to a height exceeding several feet. Due to cold-flow, the bags at the lower portion of the pile have occasionally burst under the weight of the material above it. This can lead to serious finishing and high plant clean-up losses as well as bale-to-bale adhesion and cardboard contamination.
There are many patents that disclose the use of polypropylene in connection with polymers of ethylene and propylene and in many instances, other substances, however, none of these patents disclose blending of polypropylene with raw and uncured polymers of ethylene and propylene to counteract cold-flow properties thereof. For instance, U.S. Pat. No. 3,536,653 to Bickel discloses EP rubber compositions containing extender oil and polypropylene to improve tackiness. On the basis of 100 parts of the EP rubber, amount of extender oil used is in excess of 50 parts and amount of polypropylene can vary from 2.5 to 50 parts. U.S. Pat. No. 4,086,301 to Zerpner discloses EP and EPDM rubbers containing a crosslinking agent and 5 to 100 parts of polypropylene per 100 parts of the rubber. Addition of the crosslinking agent and polypropylene is made to render the rubber readily heat-sealable. U.S. Pat. No. 3,564,080 to Pedretti discloses EP and EPDM rubbers containing a curing agent and an atactic, linear, substantially amorphous polypropylene having molecular weight of 14,000 to 48,000 as extender or diluent for the rubber which is added to the rubber on a roll mixer. Amount of polypropylene can vary from 1 to 90 parts to 100 parts of rubber.
U.S. Pat. No. 3,361,850 to Young describes a solution to the cold-flow problem of the polymers by addition thereto of up to 5% low density polyethylene. It has been confirmed that high density polyethylene does not provide the desired improvement in the cold-flow property. The problem with the polymer blends containing low density polyethylene is that products manufactured from such blends exhibit the undesirable reduction in impact strength at low temperatures. It is desirable, therefore, to overcome the cold-flow problem with respect to EP and EPDM rubbers without incurring the adverse affect relative to impact strength at low temperatures.